This invention relates generally to fuel injectors utilizing check valves, and more particularly to micrometering or varying fuel injection rates by using a variable-position check stop.
Over time, engineers have come to recognize that undesirable exhaust emissions can be reduced by having the ability to produce at least three different fuel injection rate shapes across the operating range of a given engine. These rate shapes include a ramp, a boot shape, and square fuel injection profiles. Engineers believe that by injecting a small amount of fuel just before main fuel injection to xe2x80x9cprimexe2x80x9d a fuel combustion chamber undesirable exhaust emissions can be reduced.
In addition, engineers also believe that by producing a xe2x80x9csplit injectionxe2x80x9d of varying quantities of fuel, combustion efficiency at some operating conditions, such as at idle, can be improved, and noise (especially at idle) can be reduced.
Although there exist a wide variety of mechanisms for pressurizing fuel in fuel injection systems, almost all fuel injectors include a spring biased needle check valve to open and close the nozzle outlet. In almost all fuel injectors, the needle valve member is only stoppable at two different positions: fully open or fully closed. Because the needle valve members in these fuel injectors are not normally stoppable at a partially open position, fuel injection mass flow can usually be controlled only through changes in fuel pressure.
Hydraulic bias control of the check valve is also possible, such as taught in U.S. Pat. No. 6,024,296 to Wear et al. Dual-stage spring nozzles have also been used, but these can produce slower injection rate changes than desired. Another approach is dual nozzle design, but this is an expensive solution.
It would be advantageous to have a reliable mechanism for accurately varying maximum check lift for rate shaping purposes. For example, being able to selectively reduce maximum lift of the check valve member from one shot to the next could help provide pre-metering or micrometeringxe2x80x94that is, injecting a very small amount of fuel prior to a main injection. This could improve operation of the fuel injector, especially to reduce noxious emissions and/or to reduce noise of operation, as explained above. Variable check lift could be advantageous for other purposes as well. Accurate methods of achieving very small fuel volume pre-metering or micrometering are always of interest.
The present invention is directed to addressing these and other concerns associated with controlling needle valve lift within fuel injectors.
In one aspect of the invention, a fuel injector comprises a nozzle at least partially defining a nozzle chamber and at least one nozzle orifice. A check stop in the nozzle body is comprised by a solid state motor operable to move the check stop between a protruded position and a receded position. A check valve member extends into the nozzle chamber and is slidably disposed in a nozzle body. Sliding motion of the check valve member is limited in a first direction to a closed position in which the check valve member obstructs fluid communication between the nozzle chamber and the nozzle orifice, and is limited in a second direction by the check stop.
In another aspect of the invention, a method for operating a fuel injector is disclosed. The fuel injector comprises a nozzle body including a nozzle, a check stop, and a check valve member. The nozzle at least partially defines a nozzle chamber and at least one nozzle orifice. The check stop comprises a solid state motor. The check valve member extends into the nozzle chamber and is slidable between a closed position in which the nozzle chamber is fluidly isolated from the nozzle orifice and a fully open position in which the nozzle chamber is in fluid communication with the nozzle orifice.
Pressurized fuel is supplied to the nozzle chamber. The solid state motor is operated to position the check stop at a receded position and at a protruded position. The check valve member is positioned at the closed position.
Fuel is injected from the nozzle orifice at a main injection rate by moving the check valve member to the fully open position. Fuel is injected from the nozzle orifice at a micrometering rate less than the main injection rate by positioning the check valve member at a micrometering position, between the closed position and the fully open position, in which further motion of the check valve member toward the fully open position is blocked by the check stop at the protruded position.